The doors of the payload canister are opened to transfer the space shuttle Discovery's payload into the Payload Changeout Room or PCR.

On Launch Pad 39A at NASA's Kennedy Space Center in Florida, the doors of the payload canister are opened to transfer the space shuttle Discovery's payload into the Payload Changeout Room, or PCR. The payload for the STS-119 mission comprises the integrated truss structure S6 and solar arrays to be installed on the International Space Station. They will be installed in Discovery's payload bay after the shuttle rolls out to the launch pad. Launch of Discovery on the STS-119 mission is scheduled for Feb. 12. During Discovery's 14-day mission, the crew will install the S6 truss segment and its solar arrays to the starboard side of the station, completing the station's backbone, or truss. Photo credit: NASA/Chris Rhodes